1. Technical Field
The present invention relates to a light source device, an image display apparatus, and a light amount correcting method.
2. Related Art
In recent years, as a form of an image display device, a laser scan display that raster-scans beam-like light such as a laser beam on a projection surface and displays an image attracts attention. Such a laser scan display has characteristics that, for example, contrast is extremely high compared with, for example, a projector employing a liquid crystal light valve because complete black can be represented by stopping supply of the laser beam, color purity is high because the laser beam has single wavelength, and a beam can be easily shaped (narrowed) because coherence is high. Therefore, the laser scan display is promising as a high-quality display that realizes high contrast, high color reproducibility, and high resolution.
As a laser beam source for the laser scan display, a semiconductor laser element such as a laser diode is mainly used. However, a laser characteristic of such a semiconductor laser element changes because of a temperature change, aged deterioration, and the like. Therefore, it is necessary to correct a laser beam amount such that desired image luminance can be obtained.
For example, JP-A-7-147446 discloses a technique for changing a bias current value of a semiconductor laser element by two or more points, detecting light emission power of the semiconductor laser element with light-reception-power detecting means, and detecting, for example, a change in quantum efficiency between the bias current value and a threshold current value of the semiconductor laser element to set a DC bias current of the semiconductor laser element in bias-current controlling means and set a pulse current corresponding to the change in the quantum efficiency and the like in pulse-current controlling means to maintain a level of a laser output constant. JP-A-2003-91853 discloses a technique for automatically calculating a relational expression between a detected light amount of a laser beam source and a set value of a light output, setting data of this relational expression in a light recording media driving device, and adjusting an output level of the laser beam source.
When a laser beam amount is corrected according to a change in the laser characteristic due to a temperature change or aged deterioration as explained above, in order to further improve correction accuracy, it is desirable to perform light amount correction corresponding to the change in the laser characteristic on a real time basis while actually actuating an apparatus. However, means for the light amount correction is not presented in the techniques in the past.